Presently, mainstream display interfaces are digital display interfaces. For example, AC-coupled transmission lines are used as transmission lines that are capable of transmitting digital image data at high speed. An example of a data communication system 2000 including a transmitter Tx 2100 and a receiver Rx 2200 using such a transmission line is illustrated in FIG. 12.
The transmitter Tx 2100 and the receiver Rx 2200 illustrated in FIG. 12 are connected to each other by an AC-coupled transmission line L. Capacitors C are connected in series on the transmitter output terminal sides and receiver input terminal sides of respective lines of the transmission line L. These capacitors C are used for AC coupling that blocks a Direct Current (DC) component contained in serial data being transmitted via the transmission line L.
The transmitter Tx 2100 is a circuit that transmits input serial data via the transmission line L over the amplitude of voltage set by resistors R1 and R2 and a current source I by controlling the ON/OFF operation of switches SW1 and SW2. The resistance values of the resistors R1 and R2 are all set to, for example, 50Ω, and are matched with the characteristic impedance on the transmission line L.
The receiver Rx 2200 is a circuit that receives serial data via the transmission line L using resistors R3, R4, R5 and R6 and a buffer B. The resistance values of the resistors R3 and R4 are all set to, for example, 50Ω, and are matched with the characteristic impedance on the transmission line L. The resistance values of the resistors R5 and R6 are all the same or have a predetermined voltage division ratio, and an electric potential in a voltage range which can be detected by the buffer B is set. Serial data can be stably input to the buffer B by the setting of the electric potential.
Furthermore, although FIG. 12 illustrates an example of a simplex data communication system in which serial data is transmitted from the transmitter Tx 2100 to the receiver Rx 2200, a bidirectional data communication system may be constructed by installing the same transmitter Tx and receiver Rx on each of both sides.
A conventional bidirectional display interface using an AC-coupled transmission line was disclosed in, for example, Japanese Unexamined Patent Publication No. 2008-278488. In this patent publication, there was proposed a digital display interface that enabled a plurality of data streams in different formats to be multiplexed and then transmitted.
In the conventional display interface using an AC-coupled transmission line, when the transmitter Tx starts communication from an idle state, there is a period in which a SYNC pattern is transmitted to a receiver Rx and the DC balance is adjusted. Accordingly, the period in which the DC balance is adjusted becomes an overhead. Furthermore, in the data communication system 2000 including the transmitter Tx 2100 and the receiver Rx 2200 illustrated in FIG. 12, a circuit including a plurality of resistors is provided in each of the transmitter Tx and the receiver Rx, and therefore circuit areas and power consumption are increased particularly when the data communication system 2000 is applied to a bidirectional data communication system.